Brianna went into a bakery and bought 2 cookies and 3 brownies, costing a total of $9.50. Nevaeh went into the same bakery and bought 10 cookies and 6 brownies, costing a total of $20.50. Write a system of equations that could be used to determine the price of each cookie and the price of each brownie. Define the variables that you use to write the system.